Cowling for a rotary surface aerator used for the aeration of tanks intended for water treatment

ABSTRACT

Cowling for a rotary surface aerator used for the aeration of tanks intended for the aerobic treatment of water, consisting of a skirt surrounding the aerator, wherein the skirt is made of a flexible substance or material and is ballasted in its lower part.

This application is a continuation of Ser. No. 07/880,020 filed May 8,1992 and now abandoned, which was a continuation of Ser. No. 07/672,433filed Mar. 20, 1991 and now U.S. Pat. No. 5,124,085.

The present invention relates to rotary surface aerators equippingaeration tanks used in the aerobic treatment of water, especially by theactivated-sludge process.

In order effectively to carry out such a process which involves the needfor an efficient oxygenation of the water to be treated, use is made ofaerators which are placed on the surface of the water and which executea vigorous agitation allowing air to penetrate effectively into themedium present in the tank.

These aerators consist of a turbine, the blades of which are designedand calculated so as to carry out the most efficient agitation with aminimum amount of energy, this turbine being driven in rotation by meansof a geared motor.

The aerators are mounted either on a stationary support or on a floatingassembly.

Although these aerators are efficient, they nevertheless have thedisadvantage of risking causing some nuisance, such as noise and thegeneration of mists brought about by the column of water which theyraise which are undesirable in view of their composition.

To remedy this, these aerators are surrounded by cowlings which are oftwo types:

semi-rigid or rigid cylindrical cowlings made of polyethylene or metal,or

cowlings with rigid inclined walls made of metal or polyester.

The disadvantage of the cylindrical cowlings is that they break up theenergy of the column on the vertical wall.

With a cowling having inclined walls, this disadvantage, althoughreduced, is nonetheless still present, and moreover the cost of such anappliance is very high.

The invention makes it possible to avoid these disadvantages. Itinvolves essentially producing the cowling with a skirt made of aflexible material and ballasted in its lower part.

The skirt can be in one piece, preformed and advantageouslyfrustoconical.

It can also have a tulip shape, so that its lower edge is tangent to thewater level.

Instead of being in one piece, the skirt according to the invention canconsist of a plurality of strips of trapezoidal shape, mounted on agirdle, in such a way that, when the aerator is in operation, under theeffect of the column thus produced, the skirt flares as a result of therelative sliding of its component strips on another, thesestrips-overlapping so as to ensure that the aerator is isolated from theenvironment in which it is located.

Two embodiments of the invention given solely by way of non-limitingexamples are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of this description, reference is made to the accompanyingdrawing in which:

FIG. 1 shows a general diagrammatic view of an aerator equipped with acowling consisting of a skirt according to the invention;

FIG. 2 shows a partial elevation and sectional view on a larger scale ofa first embodiment of such a skirt;

FIG. 3 shows a view, similar to that of FIG. 2, of another embodiment ofthe invention, the skirt being in the flared position;

FIG. 3a shows a partial plan view from above of the skirt in theposition of the latter corresponding to that of FIG. 3;

FIG. 4 shows a view, similar to that of FIG. 3, of the skirt which isshown there in the closed position, the aerator being inoperative;

FIG. 4a shows a plan view from above illustrating the assembly of thestrips.

As can be seen in FIG. 1, the aerator 1 comprises, fixed to a frame 2, aturbine 3 driven in rotation by means of a shaft 4 from a geared motor5.

This aerator is equipped with a cowling which, according to theinvention, consists of a skirt 6, as shown more particularly in FIG. 2,preformed in one piece from a flexible material, for example, canvas.

In this case, the skirt is of regular frustoconical shape, its upperedge being fixed to the frame 2.

Its lower edge is equipped with a ballast 7 placed, for example, in ahem belonging to the relevant edge of the skirt.

So that its lower edge can more easily be in contact with the uppersurface of the water, the lower part of the skirt can have a tulip shapeover a greater or lesser height.

The mass adopted for the ballast is determined as a function of theweight of the skirt and of the forces exerted on it.

In the embodiment illustrated in FIGS. 3, 3a and 4, the skirt, insteadof being in one piece, consists of a plurality of strips 9 made of aflexible material, such as canvas. These strips, instead of being cutstraight with the thread of the material used, such as canvas, have atrapezoidal shape and are assembled with an overlap, as shown in FIG.4a, on a girdle (not shown) fixed to the frame of the aerator.

Under these conditions, whereas the skirt is "straight", as shown inFIG. 4, when the aerator is not in operation, it flares outwardlytowards the bottom when the aerator is in operation, as shown in FIGS. 3and 3a, this occurring as a result of the sliding of its variouscomponent strips in relation to one another. In this position thesestrips overlap so as to isolate the atmosphere generated by the aeratorfrom the environment.

At all events, whatever the embodiment adopted according to theinvention, a skirt thus produced does not block the energy of thesurface current in any way, and by sliding on the column generated bythe aerator, mates with the end of this column, thus preventing it fromdiffusing into the surrounding atmosphere.

Moreover, the design of this skirt allows it to match the surface of thewater and thereby to some extent follow the variations of the latter.

Finally, the invention is especially simple and economical to put intopractice.

It goes without saying that it is not limited to the embodimentsdescribed and illustrated, but that it can give rise to variousalternative versions, without thereby departing from its scope.

I claim:
 1. A cowling surrounding a rotary surface aerator used foraerating water in tanks, said cowling comprising:a ring-shaped framelocated above the aerator and adapted to rotate therewith; a flexibleskirt for isolating the atmosphere generated by the aerator from theenvironment, said skirt surrounding the aerator and attached at an upperopen end thereof around the frame, said skirt further having an openlower end, the body of said skirt being unsupported and free of contactwith aerator components, allowing it to flare outwardly during aeratorrotation; and, ballast means attached to a lower edge of said skirt,said ballast means having a mass dependent upon the weight of the skirtfor counteracting centrifugal force exerted thereon during rotation tomaintain said lower edge at the surface of the water.
 2. A cowlingaccording to claim 1 wherein the skirt is a single frustoconical member.3. A cowling according to claim 1 wherein the lower edge of the skirt iscurved for tangential orientation with the water's surfaces.